降雨条件下坡积土边坡暂态饱和区形成机理及分布规律

降雨是引起坡积土边坡失稳的最常见外部因素之一.雨水的入渗在引起土体抗剪强度参数降低的同时,还将导致土体重度的增加、基质吸力的降低,最终造成边坡的失稳.开展雨水在边坡内部的渗流过程研究已成为分析边坡在降雨条件下稳定性的前提.基于有限元数值模拟方法,进行了雨水在土体中渗流过程的模拟,着眼于降雨条件下边坡暂态饱和区的形成、分布及消散特征,描述了该过程中边坡内部含水率、基质吸力、水力梯度的变化规律.结果表明:暂态饱和区形成的主要原因是土体中向湿润锋下方渗出的雨水量小于降雨入渗补给量,从而使得土体中的含水率累积升高;暂态饱和区的形成与降雨强度、降雨时间具有十分密切的关系,暂态饱和区形成时间、雨水入渗深度、土体表面体积含水率大小分别与降雨强度存在函数关系;清晰描述了暂态饱和区形成-发展-消散-地下水位升高的全过程,从该过程看,边坡排水措施的设计值得思考.

Formation mechanism and distribution of transient saturated areas of residual slope under rainfall conditions

Rainfall is one of the most common external factors causing the instable residual soil slope. Rainwater infiltration leads to the reduction of the soil shear strength, the increase of the weight of soil and the decrease of the matric suction, so as to cause the slope instability. The study of rainfall infiltration inside the slope has become the precondition of the study of the slope stability under the rainfall condition. Basing on the finite element numerical simulation method, this paper focuses on the simulation of rainfall infiltration process. The present work is emphasized on the formation, distribution and vanishing of transient saturated zone, and characterizes the variation of volume water content, matric suction and the hydraulic gradient inside the slope. The results can be the foundation of the study that the rainfall influences the stability of residual soil slope. The calculation results show that: 1)The major cause of the formation of transient saturated zone is ascribed to the fact that the rainwater exudation under the wetting front is less than the amount of rainfall infiltration, thus increasing the moisture content in the soil; 2)The formation of transient saturated zone, rainfall infiltration depth and the water content of soil surface have close relationship with rainfall intensity and duration. The entire process from the formation, to the development, to the vanishing of transient saturated zone, and to the raise of groundwater level is studied. From the design of slope drainage is worth thinking is indicated.